Shower base



FIG. 1 is a perspective view of a shower base showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a top plan view thereof; and,

FIG. 4 is a side view thereof.

The broken lines are for illustration purposes only and form no part of the claimed design. The broken lines adjacent to the solid lines in FIG. 4 define the bounds of the claimed design and form no part thereof. 

An ornamental design for a shower base, as shown and described. 